1At a glance
- Common Working Pressure (Aluminium)
- 200-207 bar (2,900-3,000 psi)
- Common Working Pressure (Steel)
- 200-232 bar (2,900-3,360 psi)
- Typical Capacity (Aluminium 80 cu ft)
- 11.1 litres (80 cubic feet)
- Typical Capacity (Steel 100 cu ft)
- 12.2 litres (100 cubic feet)
- Empty Buoyancy (Aluminium 80 cu ft)
- +1.8 kg (+4 lbs) positive
- Empty Buoyancy (Steel 12L)
- -1.8 to -3.6 kg (-4 to -8 lbs) negative
- Maintenance Interval (Visual Inspection)
- Annually
- Maintenance Interval (Hydrostatic Test)
- Every 2-5 years (region-dependent)
2Understanding Buoyancy Characteristics
The most significant difference between aluminium and steel tanks lies in their buoyancy profiles throughout a dive. An empty standard 11.1-litre (80 cubic feet) aluminium tank is typically positively buoyant by around 1.8 kg (4 lbs) when all the breathing gas has been consumed. This means divers using aluminium tanks need to carry more ballast weight to compensate for this eventual buoyancy, which then becomes excess weight at the beginning of the dive.
Conversely, a standard 12-litre (100 cubic feet) steel tank, whether full or empty, remains negatively buoyant, usually between -1.8 to -3.6 kg (-4 to -8 lbs) when empty. This characteristic allows divers to use less lead weight overall, as the tank contributes to the necessary ballast throughout the dive, simplifying buoyancy control, especially on safety stops.
3Aluminium vs. Steel Tanks at a Glance
| Feature | Aluminium Tanks | Steel Tanks | Impact on Diver | Liveaboard Relevance |
|---|---|---|---|---|
| Empty Buoyancy | Positive (+1.8 kg / +4 lbs) | Negative (-1.8 to -3.6 kg / -4 to -8 lbs) | More lead weight needed, especially for safety stops. | Requires divers to adjust their standard weighting setup. |
| Weight (Empty) | Lighter (11-14 kg / 24-31 lbs) | Heavier (14-16 kg / 31-35 lbs) | Easier to handle out of water, more effort underwater for trim. | Can make gearing up and re-entering the water easier. |
| Durability | Corrosion resistant, prone to dents | Stronger, prone to internal rust | Both are robust, but steel can handle more knocks. | Well-maintained tanks are essential for safety on all trips. |
| Capacity Options | Typically 80 cu ft (11.1L) standard | Often larger, e.g., 100-120 cu ft (12.2-15L) | Larger capacity offers longer bottom times. | Check availability if you need larger tanks for longer dives. |
| Common Use | Warm water, recreational, rental | Cold water, technical, experienced divers | Choice impacts personal comfort and dive style. | Aluminium is most common; steel may be an upgrade option. |
4Weight and Durability Considerations
Out of the water, a steel tank is noticeably heavier than an aluminium tank of comparable gas capacity. For example, an empty 12-litre (100 cubic feet) steel tank might weigh around 14-16 kg (31-35 lbs), while an 11.1-litre (80 cubic feet) aluminium tank typically weighs about 11-14 kg (24-31 lbs). This weight difference can impact ease of handling and transportation, particularly when gearing up on a boat or carrying equipment.
In terms of durability, both materials are robust, but steel tanks generally boast higher tensile strength, making them more resistant to impact damage and external corrosion. However, steel is susceptible to internal rust if moisture is present, necessitating careful maintenance and proper storage. Aluminium tanks are more resistant to corrosion but can be more prone to dents from sharp impacts.
5Tank Choice on Liveaboard Trips
The tank type provided on a liveaboard can significantly influence your diving experience, especially with multiple dives per day. Many liveaboards in tropical destinations typically provide aluminium tanks (e.g., 11.1-litre/80 cubic feet) due to their lighter weight for crew handling and general prevalence. If you're accustomed to steel, you may need to adjust your lead weight by adding 2-4 kg (4-8 lbs) to compensate for the aluminium tank's positive buoyancy when empty.
Some liveaboards, particularly those catering to technical divers or in colder regions, may offer steel tanks as an option or standard. If you prefer steel tanks for their consistent negative buoyancy and often higher capacity (meaning more bottom time), it's advisable to check with Blue Rides when booking your trip if steel tanks are available and if there are any associated costs or requirements.
6Common misconceptions
Myth: Steel tanks are always better because they hold more air. Fact: While steel tanks often come in larger capacities (e.g., 15 litres/120 cubic feet) compared to typical aluminium tanks (11.1 litres/80 cubic feet), capacity is not exclusive to material. Aluminium tanks are also available in larger sizes. The primary advantage of steel is its negative buoyancy, allowing for less lead weight.
Myth: Aluminium tanks are unsafe because they float when empty. Fact: Aluminium tanks are perfectly safe. Their positive buoyancy when empty simply means a diver needs to carry extra lead weight to remain neutrally buoyant throughout the entire dive, especially during the safety stop. This is a common and easily managed characteristic, not a safety flaw.
Myth: You can't use your own tank on a liveaboard. Fact: While most liveaboards provide tanks, some may allow you to bring your own, especially if you have specific requirements (e.g., sidemount, twinset, or unusual sizes). However, this needs to be coordinated in advance due to logistical and safety checks. It's best to confirm with Blue Rides or the liveaboard operator before travel.
FAQ
What type of tanks do liveaboards usually provide?
Most liveaboards, especially in tropical destinations, typically provide standard 11.1-litre (80 cubic feet) aluminium tanks. This is due to their prevalence, ease of handling for the crew, and suitability for the majority of recreational divers.
Do I need more lead weight with an aluminium tank?
Yes, generally you will need more lead weight when diving with an aluminium tank compared to a steel tank of similar capacity. This is because aluminium tanks become positively buoyant when empty, requiring extra weight to maintain neutral buoyancy throughout the dive.
Can I request a steel tank on a liveaboard?
It depends on the liveaboard. Some vessels, particularly those catering to technical divers or in certain regions, may offer steel tanks as an option, often for an additional fee or upon special request. Always inquire about tank options when booking your trip with Blue Rides.
Are steel tanks stronger than aluminium tanks?
Steel tanks are generally considered to have higher tensile strength and are more resistant to external impact damage. However, steel is susceptible to internal rust if not properly maintained, whereas aluminium is more corrosion-resistant but can dent more easily.
Which tank type is better for buoyancy control?
Many experienced divers find steel tanks offer more consistent buoyancy control because they remain negatively buoyant even when empty, meaning you carry less lead weight overall and your trim remains stable throughout the dive. Aluminium tanks require more active management of buoyancy as they lighten significantly.
What is an 80 cubic foot tank in litres?
An 80 cubic foot (cu ft) tank, a very common size in recreational diving, holds approximately 11.1 litres of breathing gas when full at its rated pressure.